The invention relates to a camshaft adjuster of an internal combustion engine, which has a locking mechanism.
In known hydraulically acting camshaft adjusters, the control times of an associated internal combustion engine are set by influencing the hydraulic relationships in control chambers, which act against each other and which act in the direction of adjustment toward an “advanced control time” and a “retarded control time.” Operation of such camshaft adjusters is not problematic when the internal combustion engine provides sufficient hydraulic pressure, so that the chambers are sufficiently filled with the hydraulic medium. However, it has been shown that when the internal combustion engine is started, under some circumstances, sufficient pressure of the hydraulic medium is not provided. This has the result that the control times do not correspond to defaults or an unstable position of the camshaft adjuster is set, whereby “unstable” control times are produced. Furthermore, undesired vibrations can be generated, which can lead to the development of undesired noise, in addition to increased component wear.
For avoiding such problems, mechanical locking mechanisms are known. From DE 196 23 818 A1, a locking mechanism is known with a locking element configured as a locking pin, whose front end region has a conical configuration and which is held, in a “locked position,” without clearance in a borehole with a conical longitudinal section or elliptical cross section in a cover of the camshaft adjuster. The locking pin is spring-loaded and has two hydraulic control surfaces, of which the first, end-side control surface is in hydraulic connection with a chamber of the camshaft adjuster and a second control surface formed by a shoulder of the locking pin is in hydraulic connection with another chamber acting in the opposite direction in the camshaft adjuster.
From DE 101 27 168 A1, a locking mechanism is known, in which a locking pin interacts with a step-shaped locking groove, wherein different plateaus of the step-shaped locking groove correspond to different locking positions, for example, an angle at the greatest advanced position, an intermediate position, and an angle at the greatest retarded position.
From DE 102 53 496, a locking mechanism is known, in which a first locking pin assumes a “locked position” between an “advanced” end position and a central position, while a second locking pin can assume a “locked position” between a “retarded” end position and the central position. If the oil pressure drops to zero, the first locking pin can be brought into the “locked position,” while the second locking pin continues to remain in the “unlocked position.” When the internal combustion engine starts up, the inner rotor is adjusted toward a “retarded” position by a dragging moment of the camshaft until the first locking pin reaches the central position. At this time point, the second locking pin also reaches the “locked position.” After the engine starts successfully, the regulator increases the oil pressure in a first oil pressure line, a first working chamber, and in the region of the first locking pin. In this way, the first locking pin is unlocked, while the second locking pin is kept in pressurized contact with the second central stop. For a transition to a regulated operation, the regulator increases the pressure in the second working chamber, by which the second locking pin is also unlocked, so that the inner rotor can move freely. A corresponding locking device is also known from U.S. Pat. No. 6,450,137 B2.
From DE 199 18 910 A1, a locking mechanism is known, which has two locking pins that can be activated in the radial adjustment direction.
From the unpublished patent application of the applicant with the internal filing number of the applicant E 2004 255 with the title “Locking mechanism for a camshaft adjuster of an internal combustion engine,” it is known to carry out locking in an end position of the camshaft adjuster with two locking pins, which feature different peripheral clearances and which are pressurized by different chambers of the camshaft adjuster.